Telephone networks have evolved greatly over the last century. From point-to-point communication to analog voice/telephone channels to the broadband digital networks of today, the driving force has been improved services for the user. As a result, greater amounts of digital data can now be sustained by a telephone network, thus offering a user a plethora of services. For example, services such as video-on-demand, call-waiting, calling line identification, conference calling, selective call rejection, distinctive ringing and many others are now available to most users.
An integrated services digital network (ISDN) provides user-to-user digital connections at 64 Kbit/s or Kbps. The original ISDN configuration has two ISDN B channels, that each carry a bit stream of 64 Kbps, and an ISDN D channel that carries signaling and user packet data. Although an ISDN B channel typically has a transfer rate of 64 Kbps on the trunks forming the direct link between the customer premises equipment (CPE), e.g., a router, and the nearest switch, through-out the network the transfer rate may be less (usually 56 Kbps). A user can avoid a wasted call, if the CPE connects at the fastest available data rate on its network. Selection of the fastest available data rate may result in a detected transfer rate of 56 Kbps.
To select the 56 Kbps transfer rate, the CPE must be configured. A user may opt to manually configure the CPE for 56 Kbps. However, this option involves time and a certain amount of technical sophistication that all users may not have nor want. A second option is to provide a means for automatically detecting the transfer rate capability of the network.
Automatic detection methods for determining a maximum transfer rate, to date, have led to increased delay, larger network loads, and increased costs to users. Other automatic detection methods that rely on cause codes from the switches in the network are ultimately unreliable, because the cause codes for the network may be changed externally without the CPE recognizing that a change has occurred. In such cases, calls may be rejected unnecessarily.
Basic-Rate Interface is the basic ISDN configuration. This configuration consists of two B-channels (bearer-channels) that can carry voice or data at rate of 64 Kbps, and one D-channel (data-channels), which carries call-control information. Another type of ISDN configuration is called Primary-Rate Interface (PRI), which consists of 23 B-channels (30 in Europe) and one D-channel. Callback is a method used in ISDN line communications which charges the cost of a call on the network to a specific party, regardless of which party initiated the call. A party “Alpha” calling a party “Omega”, can ask “Omega” to call her back. Normally, such a situation occurs automatically via point-to-point connections within an established B-channel. Inbound signaling, upon establishment of the connection, proceeds to signal to “Omega” that Alpha requests a callback, whereupon Alpha or Omega hangs up. Subsequently, Omega calls back.
A second option is usually referred to as D-channel callback and involves, in the above example, configuring Omega's equipment to recognize incoming calls from a certain party. Upon recognizing the specific incoming party's call, Omega's equipment is programmed to terminate the incoming call and call the incoming caller back within a fixed time period. A problem is encountered when the incoming call is terminated. At the far end, i.e., Alpha's end, the termination is not received immediately. There is an inherent delay of at least four seconds because of the ISDN protocol. As a result of the delay, Omega has to wait at least four seconds to call back, otherwise the line might be busy and the call will fail. If this is encountered, the router placing the callback must retry the callback operation.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for systems and methods to detect and adapt to varying network transfer rates. In addition, a system and method is needed to reduce the callback retry operations and minimize the delay associated with a callback.